Magnet core built up from titanium-containing manganese-zinc-ferrous ferrite and method of manufacturing the same

ABSTRACT

A MAGNET CORE HAVING A TEMPERATURE FACTOR OF THE EFECTIVE MAGNETIC INITIAL PERMEABILTIY WHICH IS SUBSTANTIALLY CONSTANT OVER AN EXTENSIVE TEMPERATURE RANGE, ESPECIALLY SUITABLE FOR USE IN INDUCTANCE-CAPACITANCE FILTERS IN WHICH POLYSTYRENE CAPACITORS ARE USED. THE TEMPERATURE VARIABILITY OF THE CAPACITY OF THE CAPACITORS IN QUESTION MAY THEN BE COMPENSATED FOR BY THE TEMPERATURE VARIABILITY OF THE FILTER COILS, IN WHICH THE MAGNET CORES ACCORDING TO THE INVENTION SERVE AS CORE BODIES. THE MAGNET CORES ACCORDING TO THE INVENTION CONSIST OF A FERRITE MATERIAL HAVING A COMPOSITION LYING WITH THE FOLLOWING RANGE OF CONCENTRATION LIMITS OF THE FIVE-COMPONENTS SYSTEM MNO-ZNO-FE2O3-TIO2-FEO:   27-40 MOL. PERCENT MNO 8-16 MOL. PERCENT ZNO 40-49.5 MOL.PERCENT FE2O3 0.5-7, PREFERABLY 2-L MOL. PERCENT TIO2 3-7.5 MOL. PERCENT FEO.   THESE CORES ARE MANUFACTURED BY MIXING MNO, ZNO, FE2O3 AND TIO2, OR COMPOUNDS WHICH DECOMPSE UPON HEATING TO FORM THOSE OXIDES IN PROPORTIONS YIELDING UPON SINTERING THE AFORESAID MATERIALS, COMPACTING THE OXIDE MIXTURE INTO CORES WCHIC ARE HEATED TO BETWEEN 1100*C. AND 1450*C.FOR 30 TO 60 MINUTES AND THEREAFTER COOLING IN AN ATMOSPHERE CONTAINING SPECIFIED QUANTITIES OF OXYGEN.

Feb. 29, 1972 J. KLERK ETAL 3,645,898

MAGNET CORE BUILT UP FROM TITANIUM-CONTAINING MANGANESE-ZINC-FERROUSFERRITE AND METHOD OF MANUFACTURING THE SAME Filed April 50, 1969 021010; 0 (in atm) 2 (TinK) INVENTORS JACOB KLERK THEODORUS G.W. STUNT'JES.MGEN

States Patent Claims ABSTRACT OF THE DISCLOSURE A magnet core having atemperature factor of the ellective magnetic initial permeability whichis substantially constant over an extensive temperature range,especially suitable for use in inductance-capacitance filters in whichpolystyrene capacitors are used. The temperature variability ofthecapacity of the capacitors in question may thenbe compensated-for bythe temperature variability .Qfjthe filtercoils, in which the magnetcores according to the invention serve as core bodies.

The magnet cores according to the invention consist of a ferritematerial Having a composition lying within .the following range ofconcentration limits of the five-components system MnO'ZnO--Fe O TiO-FeO: 27-401lino1, percent MnO- ,8-16 mol. percent ZnO 40-49 5 mol.percent Fe O '0.'5-7,' preferably 2-6 mol. percent T 3-7.5 inol. percentFeO.

These cores are manufactured by mixing MnO, ZnO, 'Fe O land' TiO orcompounds which decompose upon heating to form those oxides inproportions yielding upon .sintering the aforesaid materials, compactingthe oxide mixture into cores which are heated to between 1100 C. and1450 C. for '30 to 60 minutes and thereafter cooling inanatmospherecontaining specified quantities of oxygen.

In carrier wave telephony, inductance-capacitance filters (so-calledLC-filters) are frequently used for realizing separate frequency rangeson behalf of the various channels. The limit value of the frequency atwhich the damping of the filter with varying frequency begins toincrease rapidly "(which limit'value Will'be denoted here by the symboli is allowed to vary only slightly with the temperature, since otherwisethe channels partly overlap each other so that mixing of speechesoccurs. This limit value,

" f,,,' is" determined by the resonance frequencies (f,) of the LCcircuits in the filter. For the resonant frequency the ;relation 1 T t f.f

holds, in which 1, is the resonance frequency in c./ s. (Hz) L is theinductance of the filter coil expressed in H (Henry) and C is thecapacity of the filter capacitor ex pressed in F (farad). For asubstantially temperatureindependent frequency of the LC filter, asubstantially .temperature-independent value of the product LC is hencerequired.

For use as a dielectric for the capacitors of the filters in questionthe material polystyrene has several advantages, inter alia thecomparatively low price and the com- .pa ratiyelylow loss factor (tanI-Iowever, the temperature coefiicient of the capacity (C) of apolystyrene capacitor is approximately 10- per C. In order to be able touse the said polystyrenecapacitors all the same in the said LC-filters,it is necessary to combine said capacitors with coils the temperaturedependence of which 011 the inductance (L) approximately compensates forthat of the capacity, C, of the capacitor so that the product LC of theLC-circuits of the filter does again substantially not vary withtemperature.

In connection with the endeavours to restrict the dimen sions of thechannels apparatus as much as possible, one has proceeded to theconstruction of smaller and smaller filter coils. This again results inendeavours to increase the effective magnetic permeability of themagnetic coil core towards higher values. In order to be able to use theabove-mentioned polystyrene capacitors all the same, the coil core musthave an adjustable, substantially constant, temperature coetficient (TC)of the effective magnetic initial permeability (,u over an extensivetemperature range. In order to reach the correct temperature coefficientof the coil, there is started from the temperature factor (TF) of thecoil core. The temperature factor is defined by the formula in whichformula (,uQ is the value of the effective magnetic initial permeabilityof the magnet core in question at the temperature t while h is the valueof the magnetic initial permeability at the reference temperature t Whenthe length of the air-gap in the magnet core is zero, h is the magneticinitial permeability of the magnet core material at the temperature tRoom temperature is generally chosen as the reference temperature. Therelationship between the quantities TC and TF is represented by theequation (TC=TFx ,u

The invention provides a new class of magnet cores which provides forthe above described need. The said magnet cores which are constructedfrom titanium-containing manganese-zinc-ferrous ferrite arecharacterized on the one hand by a substantially constant temperaturefactor, which is adjustable at a given desired value over an extensivetemperature range, and on the other hand by a composition within therange defined by the following limit values of the molar percentages ofthe metal oxides:

27-40 mol. percent MnO 8-16 mol. percent ZnO 40-495 mol. percent Fe O0.5-7 mol. percent TiO 3-7.5 mol. percent FeO The limits of the titaniumcontent are preferably chosen in accordance with a content of from 2-6mol percent TiO It is to be noted that the molar percentages of FeOstated above are based on the supposition that all the manganese presentin the ferrite is bivalent and all the titanium present in the ferriteis tetravalent.

The manufacture of the magnet cores according to the invention iscarried out according to methods commonly used in manufacturing ferritemagnet cores in which a (usually prefired mixture of the oxides of theferrite-forming metals (of which oxides one or more can be replacedfully or partly by one or more other compounds of the metals in questionwhich are converted into said oxides upon heating) is compressed to thedesired shape and then heated at a temperature above 1000 C. 1

According to the invention, the mixture which is com pressed to thedesired shape is heated (and hence sintered) in an oxygen-containingatmospherei'to a. temperature maximum between"1'100 C. "and 1450 C. Thesaid temperature maximum is preferably maintained for a period of timeof from 30 minutes to 60 minutes.

It is recommendable, both during maintaining the temperature maximum andduring the subsequent cooling of of purity of the raw material and thecondition that during grinding a little iron is taken up by the mixturesas a result of wear of the grinding apparatus (so-called ground-in iron)were taken into account. The quantity of ground-in iron is a function ofthe duration of grinding the shaped sintered body, to adapt the partialoxygen pressure, p of the atmosphere in which heating and and for thegiven griding aggregate it is determined precooling takes place to thetemperature prevailing in said viously empirically. One or more seriesof rings were atmosphere in accordance with directives known forcompressed from each of the reground prefired mixtures, similar cases(for which purpose see, for example, British said rings having anoutside diameter of 14.8 mm., an patent specification No. 891,131). Inthis connection refinside diameter of 7.4 mm. and a height of 6.5; mm..Each erence is made to the drawing which is a diagram in series wasthen heated up to the sintering temperature in which the reciprocalvalues of the temperature T, exan oven which was provided with a controlapparatus 'for pressed in degrees Kelvin are plotted on the horizontalthe partial oxygen PTBSSIIIE P0 which pe ature was axis and the values fthe logarithm to the ba e ten, then maintained for approximately 45minutes. The sin- 1081 027 015 the P t l Oxygen pre expressed in atteredrings were then cooled in and with the oven. At the mospheres areplotted on the vertical axis. The adaptasintering p ature a during t esubsequent Q I g tion of the partial oxygen pressure to the temperaturethe partial oxygen pressure of the oven atmosphere was is carried outpreferably in such manner that for sinteralways adapated to thetemperature prevailing said atmosing and cooling of a given oven load,the values of phere so that the relationship I 10 125 and l/T associatedwith each other are situated 61 on a straight line which, subject tobeing elongated suffi- 015gPo 2 ciently far, if required, intersectsboth the straight-line section A-B and the straight-line section CD. Thelocawas satisfied, which T is the temperature in K. during tion of thediagram points A, B, C and D appears, sintering and cooling, while 0 andc areconstants for besides from the above-mentioned diagram, from theeach series of rings with the treatment'and co usedfollowing Table G.During the treatment of the first series of rings, the sinter- TABLE Ging temperature was 1220 C. while the partial oxygen pressure of theoven atmosphere was controlled so that T (in gags 10mg 5;; the linearrelationship T p ere P02 points 39 14314 H 1,423 0.001 1/l,423 -3 A 2l'ggg +033 3 was satisfied D So in this case 5,:14314 and 5 :782. In thediagra An even more accurate adaptation can be realized by shown Insaild linear relationshlp represemlad by ensuring that theabove-mentioned straight line, it again F graph fg i i 1 i l i elongatedsufliciently far, if required, intersects both the me secnops and 1S i aso sans es e (more stringent) requlrement that 1t 1ntersects the lmestraight-lme-sectlon -EF and the stra1ght-l1ne section section locatlonof i diagram Pomts and F A total of 7 series of rings were processed tomagnet reference 1s made to the d1agram 1tself and also to the cores inthe above described manner In the following Table H below table K thesintering temperature, the control of the par TABLE H tial oxygenpressure of the oven atmosphere as a function pm (in 015 the temperatureduring sintering and during cooling, T (in atmos- 10/1og gram t eindication of the associated graph in the drawing, and T (mg C) c K)pheres) 1/ T pm Points 45 the composition of the resulting magnet coresexpressed 1,350 11623 1/11623 in molar percentages of the oxides MnO,ZnO, LFe O 1350 1623 1/1623 P T10 and FeO is stated for each series of,rings.

TABLE K ln g t e fr r Control partial I V pg; oxygen pressureComposition (molecular percent) Series Number 0.) 01 Graph M110 ZnO FeOa TiO FeO 1,220 14,314 7.82 a 37.5 9.3 41.0 6.1 6.1 1,220 20,500 11. 35B 32.5 12.7 48.2 1.2 5.4 1,220 16,457 9.44 'y 35.6 10.6 43.7 4.3 5.81,250 16,457 9.44 'y 35.6 10.6 43.7 4.3 5.8 1,400 12,173 6.20 6 35.011.0 44.0 3.7 5.7 1,250 16,457 9.44 v 35.0 11.0 44.6 3.7 5.7 1,22014,314 7.82 or 35.0 11.0 44.6 3.7 5.7

In order that the invention may be readily carried into effect, oneexample thereof will now be described in detail. A number of mixtures ofmanganese carbonate MnCO ferric oxide, Fe O zinc oxide, ZnO, andtitanium dioxide, TiO differing mutually in quantitative compositionwere weighed in. These mixtures were ground, dried, prefired (forexample, by heating in air for 4 hours) cooled and ground again. Uponweighingin the degree The graph 7 just intersects the point B while thegraph 5 just intersects the point F. i I

The principal magnetic quality values, measured in the resulting magnetcores are recorded inthe followingtable L. The first, extreme left,column of said table contains the numbers of the series (see table K),from which the magnet cores in question were prepared. In the secondcolumn are stated the values of the initial permeability in which is themagnetic initial permeability minutes after demagnetization of the coreand 9 is the same quantity 100 minutes after demagnetization of thecore, the sixth column states that of the resistivity p expressed inohm. cm., while the last, extreme right, column indicates the Curiepoint values.

heated and cooled in an atmosphere having a partial oxygen pressure psatisfying the condition,

in which T is the temperature in K. and C and C are constants the valuesof which are such that at a value of p =0.001 atmosphere, thetemperature is bet-ween 950 C., and 1150 C. and that at a temperature of1450 C., the value of p lies between 0.026 and 3.3 atmospheres.

2. A method as claimed in claim 1 wherein the values of the constants Cand C are such that at a temperature of 1350 C. the value of p isbetween 0.05 and 0.2 atmospheres.

3. A method as claimed in claim 1 in which the oxides are mixed inproportions forming upon heating a core consisting of:

27-40 mol percent MnO TABLE L Temperature factor t gaxlo m (ohmp SeriesNo. In Temperature trajeet TFX10 (10011112.) DF 10 cm.) C.)

1 1,470 {3 2% Eilfllrf6 6133jj13 iii} 2 1,000 205 2 000 5 31, {g} 4.4 3550 200 a 1,400 ;gg:

4 1, 500 $338; 2.3 2 2,400 200 6 1,810 1333 $531133: 8:; 8:2} 3.1 1 1,1200 0 1, 3 0 13338 3}} {g} 2.0 a 2,400 200 7 1,480 {;gg:g 3}} 3} 2.2 22,000 200 The measured values of tan 8 DF and p stated in the Table Lrelate to measurements performed at room temperature C.).

Upon providing the air-gap in the magnet cores, the effective initialpermeability, ,u can be adjusted so that when the core is used in anLC-circuit with polystyrene capacitors the best temperature compensationis realized. As already stated, the temperature coefficient of apolystyrene capacitor is approximately 150 X l0 per C. So thetemperature compensation aimed at is achieved when the requirement 150 X10 l e T F is satisfied, in which T F is the temperature factor of themagnet core. For example, for the magnet cores prepared from series 4,with a TF of 1.5 x 10 the value 100 is the value of the effectiveinitial permeability which is most favourable for a good temperaturecompensation.

What is claimed is: 1. A method of manufacturing a magnet core having asubstantially constant temperature factor of the effective magneticinitial permeability over a temperature range extending from 90 C. to+180 C. comprising the steps of forming a mixture of MnO, ZnO, Fe O andTiO in proportions forming upon heating a core consist ing of:

27-40 mol percent MnO 8-16 mol percent ZnO 40-495 mol percent Fe 0 0.5-7mol percent TiO and 3-7.5 mol percent FeO, compacting said mixture intoa core, heating said core to a temperature between 1100 C. and 1450" C.,maintaining said core at said temperature for about 30 to 60 minutes,and thereafter cooling said core, said core being 8-16 mol percent ZnO40-495 mol percent F e 0 2-6 mol percent TiO 3-7.5 mol percent FeO.

4.. A magnetic core having a substantially constant temperature factorof the effective magnetic initial permeability over a temperature rangeextending from C. to C. and a composition consisting of:

27-40 mol percent MnO 8-16 mol percent ZnO 40-495 mol percent Fe O 0.5-7mol percent T10 and 3-7.5 mol percent FeO,

said core being made in accordance with the method as defined in claim1.

5. A magnetic core having a substantially constant temperature factor ofthe effective magnetic initial permeability over a temperature rangeextending from 90 C. to 180 C. and a composition consisting of:

27-40 11101 percent MnO 8-16 mol percent ZnO 40-495 mol percent Fe O 2-6mol percent TiO and 3-7.5 mol percent FeO. said core being made inaccordance with the method as defined in claim 1.

References Cited UNITED STATES PATENTS 3,027,327 3/1962 Blank 252-62623,106,534 10/1963 Akashi et al. 25262.59' 3,154,493 10/ 1964 Pierrot etal. 252-6262 3,492,236 1/1970 Ross 25262.59

TOBIAS E. DEVOW, Primary Examiner J. COOPER, Assist-ant Examiner U- S-Cl. .R. 252-6262

